The present invention relates to an electronic unit having a circuit board (PCB) arranged to be mounted in a main housing. The main housing has a first housing part and a second housing part, where the first housing part at least partly is electrically conducting. The PCB has a first outer layer, a second outer layer and a ground plane, where the first outer layer mainly faces the first housing part and the second outer layer mainly faces the second housing part when mounted.
In several technical fields, for instance in the control of electrical systems on board a motor vehicle, it is desirable to provide a sealed housing with a cover containing a PCB (Printed Circuit Board), onto which are mounted several electronic components. Such a sealed housing containing a PCB with electronic components is for example known as an ECU (Electronic Control Unit). The sealed housing with its cover protects the PCB and its components against mechanical damage and various environmental influences.
It is also desirable to obtain electromagnetic shielding or to improve EMC (Electromagnetic Compatibility). For example, the PCB is normally provided with a plug connector for making electrical contact between the ECU and other parts of the vehicle when mounted. Such a connector is a source of EMI (Electromagnetic Interference) since the connector's leads act as antennas that both transmit and receive signals, and it is therefore desired to keep the connector separates from components sensitive to EMI as well as components which emit EMI.
In U.S. Pat. No. 5,392,197 it is disclosed that the housing and its cover may be made in metal in order to shield all components of the ECU.
However, here no shielding between separate components which may disturb each other is disclosed, and the metal housing and cover is expensive and bulky.
In WO 2011069828 it is disclosed to use separate metal covers that shield certain components, which covers also may act as thermal conductors for heat dissipation.
However, here a number of separate metal covers that are specially shaped and need special mounting are needed.
There is thus a need for an ECU with an EMI shielding that is more versatile than prior solutions and which is uncomplicated to assemble, neither inflicting higher material costs, nor causing a more complicated assembly.
It is therefore an object of the present invention to provide an ECU with an EMI shielding that is more versatile than prior solutions and which is uncomplicated to assemble, neither inflicting higher material costs, nor causing a more complicated assembly.
This object is achieved by means of an electronic unit having a circuit board (PCB) arranged to be mounted in a main housing. The main housing has a first housing part and a second housing part, where the first housing part at least partly is electrically conducting. The PCB has a first outer layer, a second outer layer and a ground plane, where the first outer layer mainly faces the first housing part and the second outer layer mainly faces the second housing part when mounted. Furthermore, when mounted, the ground plane is arranged to make electrical contact with the first housing part such that a first chamber, facing the first outer layer, and a second chamber, facing the second outer layer, are formed, where said chambers are separated by means of the ground plane, such that an electromagnetic shielding is created between the chambers.
According to an example of the present invention, the first housing part is made in a metal material and the second housing part is made in a plastic material.
According to another example of the present invention, the electronic unit further has a connector arranged for establishing electrical contact between the electronic unit and parts outside the electronic unit. The connector has a number of connector pins and at is least partly positioned in the second chamber. Preferably, the connector is press-fitted between the first housing part and the second housing part, and an electromagnetic interference (EMI) filter arrangement may be positioned at the connector pins.
According to another example of the present invention, a first plurality of components is mounted on the first outer layer and a second plurality of components is mounted on the second outer layer. All components of one layer are mounted in a re-flow process and at least one component on the other layer is mounted by means of another process. Said other process is for example one of press-fit, gluing or bonding.
Further examples of the invention are described in this specification.
A number of advantages are obtained by means of the present invention, for example an EMI shielding may be obtained without increasing the number of parts used for the electronic unit.